Source attribution of human salmonellosis and campylobacteriosos using a systematic review of studies of sporadic infections

Salmonella spp. and Campylobacter spp. are widespread and important causes of human illness worldwide. Disease is most frequently associated with foodborne transmission, but other routes of exposure, such as direct contact with live animals and person-to-person transmission, are recognized. Identifying the most important sources of human disease is essential for prioritizing food safety interventions and setting public health goals. Numerous case-control studies of sporadic infections of salmonellosis and campylobacteriosis have been published. These studies investigate a variety of potential risk factors for disease, and often use different methodologies and settings. Systematic reviews (SR) consist of a formal process for literature review focused on a specific research question, and include the identification of relevant literature, quality assessment of relevant studies, summarization or statistical analysis of data, and conclusions. With the objective of identifying the most important risk factors for human sporadic salmonellosis and campylobacteriosis, we performed a SR of case-control studies and meta-analysis of the obtained results. From 1,295 identified references, 132 passed the relevance screening, 73 passed the quality assessment stage, and data was extracted from 72. Of these studies, 34 investigated risk factors for human salmonellosis and 37 focused on campylobacteriosis. Heterogeneity between the studies and possible sources of bias were assessed. Information on exposures of cases and controls, and estimated odds ratios for investigated risk factors were recovered and analyzed with the purpose of assisting attribution of human disease. The most significant results were illustrated using forest plots.